cycling a new tank

[Bloodasp]

Go for as much as you can afford without overfilling the tank of course. About 60-80 lbs depends on how light the rocks are. That would also give you a better idea on how the rocks will go together rather than buying one at a time and ending up with a few leftover that somehow don't fit, you can always cement or glue them together but still that would be a lot of cutting and drilling just to get them to stay where you want.